1. Field of the Invention
This invention relates to magnetic sensor devices using magnetic resistive effect type elements, and more particularly, to magnetic sensor devices for reproducing signals such as those representing position codes recorded on a medium whose reading channel code is plural, or at so-called multi-tracks.
2. Description of the Prior Art
The magnetic sensor devices for use in reading code signals, such as those representing positions recorded on magnetic recording media by using a plurality of elements having the magnetic resistive effect (hereinafter referred to as the "magnetic resistive effect type" element) arranged in a row on a substrate, are known as the position detector or the like. In this kind of device, the code signals are read out electrically in the form of a change of resistance of that element for the purpose of detecting the absolute position of an object bearing the magnetic recording medium.
FIG. 1A illustrates an example of the prior known magnetic sensor device wherein the device is generally indicated at 1, operating with a magnetic recording medium 2 having a multiple channel to record signals in Gray Code form, 4a and 4b representing the least and most significant bit code signals, respectively.
Four magnetic resistive effect elements 1A to 1D are buried at the bottom of a substrate 10 and are arranged to face at respective channels. Each of the elements 1A to 1D has output lines on either side thereof. A bias line 5 is provided on the substrate 10 and its arrangement is such that all the elements 1A to 1D are biased by an equal magnetic field to each other.
In such a prior known device, on assumption that the code signals 4a . . . 4b on the magnetic recording medium 2 takes the magnetized form in a direction parallel to the thickness of the medium 2 with the N and S poles being farther and nearer from and to the base of the medium 2 as shown in FIG. 1B, it may be considered that a neighboring point P1 to the code signal on the recording medium 2 is magnetized to S pole.
In FIG. 1B, the code signal 4a having magnetic recorded elements 4a1, 4a2, . . . is scanned when the magnetic resistive effect (MR) element 1A moves past successive points P1 to P6.
P1 is an intermediate point between the recorded elements 4a1 and 4a2.
P2 is a point at the initial end of the recorded element 4a2.
P3 is a point the MR element 1A arrives at after having advanced 1/4 from the initial end of the recorded element 4a2.
P4 is a point when the MR element 1A has come to the center of the longitudinal length of the recorded element 4a2.
P5 is a point when the MR element 1A has advanced 3/4 on the recorded element 4a2.
P6 is a point when the MR element 1A has come to the terminal end of the recorded element 4a2.
Plotting the values of voltage at the output of the aforesaid MR element 1A against the individual points P1 to P6 in position and smoothly connecting these plotted points, we obtain a curve shown in FIG. 2A. By subjecting the output signal of the magnetic sensor device 1 to inversion when in signal processing, the curve of FIG. 2A is changed to a one shown in FIG. 2B.
Here, the waveform of FIG. 2B can be related to the magnetic recorded elements the MR element 1A has scanned as shown in FIG. 2C. A portion "y" of the waveform of FIG. 2B represents an output signal which occurs when no magnetic recorded element is scanned, so to speak, an unnecessary signal. This "y" signal, when it actually comes out in the output of the MR element, gives an influence on the accuracy of detection of the position by the MR element.
The method of removing this unnecessary "y" signal is to apply a magnetic field as the bias to the MR element. For this purpose, as shown in FIG. 1A, the MR elements for scanning the magnetic recorded elements are provided with a bias line 5 to give them a bias magnetic field. When the MR elements are biased to S pole of magnetic field, the S pole between the successive two recorded elements on the medium 2 is cancelled so that it can no longer be detected as a component of the output of the MR element.
From the foregoing reason, the magnetic sensor device has means for generating a bias magnetic field as shown in FIG. 1A. In case when the signals to be read are spread over a plurality of tracks, or are of the multi-track type, the use of a uniform intensity distribution of bias magnetic field over all the MR elements gives rise to a problem. That is, a bias which is proper to the signal 4a of the least significant bit in FIG. 1A for enabling to erase the signal components appearing between the recorded elements (FIG. 4A) becomes improper for the signal 4b of the most significant bit. This is because the size of the area of the magnetic recorded element for the signal of most significant bit 4b is larger, and its magnitude of magnetic field acting on the MR element 1D is larger than that of magnetic field of the signal 4a of least significant bit on the MR element 1A, and, therefore, because the S-polarized magnetic field between the successive two magnetic recorded elements for the signal 4b of the most significant bit is also larger. For this reason, the magnitude of magnetic field of the bias that is optimum to the signal 4a of least significant bit cannot cancel all of the S-polarized magnetic field at an intermediate point between the magnetic recorded elements for the signal 4b of the most significant bit. As a result, the output of the MR element for the signal 4b of the most significant bit includes a spurious signal "y" arising from between the recorded elements.